Low pressure venting panels in accordance with the present invention are often used in conjunction with dust collecting equipment, such as bag houses, employed to collect milling dust and the like. Such bag houses are subject to the risk of explosion inherent in dust collection and several such catastrophic explosions occur annually in the United States. Bag houses and the like are generally not rigidly constructed and able to withstand the force of uncontrolled explosions. Thus, vessels such as bag houses require pressure relief safety devices which rupture at relatively low pressure yet predictably rupture so as not to undesirably vent dust into the atmosphere and thereby violate various governmental regulations regarding air pollution.
Early devices for providing vent openings in bag houses and the like include burstable membranes or panels of various types, such as roofing paper, cloth, plastic and metal foils. Some membranes or panels were scored to provide lines of weakness; however, reliability, predictability of burst pressure and adequate opening for proper venting was often unsatisfactory.
In other applications requiring predictable low pressure venting, gaseous processes in large tanks are often subject to explosion or failure. Such tanks are often expensive, the process expensive, and relief devices must be predictable in operation at low pressures.
In an effort to provide predictable low pressure rupture panels or discs, two designs have been heretofore developed. A first rupture disc design is termed a composite disc and utilizes a thin, floating flexible sealing member in conjunction with a slotted metal member. However, this design has been subject to poor cycling life, relatively inaccurate burst pressures and fragmentation which may clog downstream conduits or provide shrapnel like projectiles upon violent rupture. The composite disc has a central burst point aperture and cut slots to ensure opening in the form of leaves and lack of fragmentation. In this disc, a thin, very flexible sealing membrane is disposed beneath a metal top section. The mechanics of rupture involve swinging out of the metal top section until the thin flexible seal expands uncontrollably and rips open in an undefined tear line. This disc structure has inherent design deficiencies in that the slots in the metal top section greatly weaken the metal and cause the top section to be quite flimsy and move up and down in response to process pressure pulsations. This cycling movement induces fatigue and greatly reduces useful life. The addition of a vacuum support or backing member has done little to alleviate fatigue in the metal sheet.
Further, the use of the thin flexible steel creates problems in that the seal tends to balloon through the slots and fails under tension along relatively undesignated lines.
A second design of a low pressure rupture disc, as disclosed by Fike U.S. Pat. No. 4,067,154, uses a solid piece of metal with taped lines and a flexible coating. The burst pressure is determined by the thickness of the metal and the thickness and type of coating. The tape defines sharp-breaking, shear burst lines in the panel. However, this design is also believed to yield relatively inaccurate and difficult to predict burst pressures. Further, this disc also experiences cycling problems which lead to metal fatigue and premature failure.
The low pressure venting panel of the present invention preferably includes a thin rupture body having a central group of apertures and slits through the body emanating from the aperture or apertures. A sealing membrane of semi-elastic or relatively inflexible material is bonded to the rupture body at least in the area of the slits. The sealing membrane resists expansion in the area of the slits when the pressure is applied to the rupture body, thereby resisting rupture of the membrane up to the design rupture limit of the venting panel.